A Phase I SBIR program has been completed to develop an assay system for rapid screening of patients prior to initiation of thrombolytic therapy. This system is based on a novel dry reagent assay technology which has been applied successfully to PT and activated PTT tests and requires a single drop of freshly drawn whole blood as a sample. The drug challenge assay system was developed further during the Phase I program, and its potential was demonstrated using a combination of laboratory studies and clinical sample studies. Early determination of in vitro clot lysis response in patients prior to thrombolytic therapy was explored. Further development during the Phase II program will focus on: pilot production of test cards; finalization of analyzer software; development of quality control methods; and determination of test performance characteristics. Major activities will include: performing clinical studies; developing a kinetic model for the test system; analyzing clinical data; determining of the best utilization of the assay system and its potential impact. Testing in clinical environments will be performed in conjunction with Research Triangle Area Medical Centers.